Field of the Invention
The present invention relates to a focal-plane shutter used for image capturing apparatuses such as digital cameras.
Description of the Related Art
Focal-plane shutters used for cameras includes two blade groups (a leading curtain and a trailing curtain) each connected to a blade drive member and moved by the blade drive member rotated by a driving force so as to open or shut an aperture.
In such shutters, after the movement of the blade group, the blade drive member may hit a mechanical movable end to bounce and thereby the blade group may be moved back from its original movement completion position to a position affecting an exposure of an image sensor. Therefore, such a problem due to the bounce of the blade drive member is required to be avoided. Thus, the shutters are often provided with a brake mechanism to reduce a speed of the blade drive member or a lock mechanism (bounce reduction mechanism) to lock the blade drive member so as to reduce its bounce.
Japanese Patent No. 4334092 discloses a focal-plane shutter provided with brake and lock mechanisms. This shutter causes a leading curtain drive member that drives a leading curtain, before completion of a movement of a trailing curtain, to move a brake member into a rotatable area of a trailing curtain drive member. Then, the brake member is deformed by contact of the rotating trailing curtain drive member and thereafter returns to its original shape, thereby reducing a speed of the trailing curtain drive member (that is, of the trailing curtain) and locking the trailing curtain drive member.
However, the brake member in the shutter disclosed in Japanese Patent No. 4334092 has flexibility (elasticity), so that, when the trailing curtain drive member has high motion energy at the completion of the movement of the trailing curtain and thereby a bouncing force thereof is large, the brake member cannot sufficiently reduce the bounce of the trailing curtain drive member.
Furthermore, when a fast shutter speed is set and thereby a difference between movement completion times of the leading and trailing curtains is small, the brake member that is located in the rotatable area of the trailing curtain drive member but whose position is unstable contacts the trailing curtain drive member, which makes the lock of the trailing curtain drive member unstable.